Commonly used automotive vehicle differentials generally comprise a housing which is gear connected to the vehicle engine drive shaft for rotating the housing. Bevel gear arrangements within the housing transmit the torque equally to both of the driven wheel axles. These axles have inner ends that extend into the housing and outer ends connected to the wheels. The differential gearing permits the speeds of the driven shafts to change according to demand. However, in these conventional differential assemblies, when the traction of either wheel is zero, such as when the wheel is spinning on ice or snow or mud, there is no power or torque transmitted to the opposite wheel so that it remains stationary.
Various types of limited slip differentials have been developed in the past for the purpose of powering one wheel during the time that the other wheel spins, that is, has lost its traction. An example of one form of such a power dividing or limited slip differential is disclosed in my prior U.S. Pat. No. 2,720,796 issued Jan. 18, 1955.
Another type of differential includes a locking means which normally locks both axles to the power rotating housing for equal rotational speed of the driven wheel axles, but wherein, when one of the axles rotates faster than the other, such as the one located on the outside curve during turning of a vehicle, that axle is momentarily disengaged and permitted to free wheel while the other axle receives the torque. Examples of this kind of locking differential are described in U.S. Pat. No. 1,275,952 to Luxmoor issued Aug. 13, 1918, and U.S. Pat. No. 1,477,311 to Cartwright issued Dec. 11, 1923, U.S. Pat. No. 2,060,558 to De Lavaud issued Nov. 10, 1936 and U.S. Pat. No. 2,179,923 to De Lavaud issued May 27, 1937. Another example of that general type of locking differential is disclosed in my co-pending patent application, U.S. Ser. No. 306,833 filed Sept. 29, 1981.
These locking differentials, in general, comprise an assembly of a central driving member which is connected to, and rotates with, the rotating housing and which is releasably coupled to driven pressure plates located on opposite sides of the driving member. The pressure plates, in turn, are coupled to the axle ends through clutches or couplings.
During normal operation, such as on a straight path of movement of the vehicle, the rotating driving member drives both of the pressure plates through their couplings. Likewise the pressure plates drive both of the axles eqully through their couplings. However, when one axle overruns the other, such as during the time that one wheel rotates faster than the other while the vehicle travels around a curve, the over-running axle causes its pressure plate to uncouple from the driving member so that the axle can freewheel, until it returns to the speed of the other axle.
The invention herein relates to this latter kind of locking differential, that is, a differential wherein either axle is uncoupled from the power source during the times that it rotates faster than the other axle and the housing. However, the assembly of this invention is simplified and very compact so that it may be utilized with existing vehicle diferential housings. That is, it may be substituted for the mechanism which otherwise would have been used within that conventional housing. Thus, in the case of certain vehicles, such as trucks, conventional differentials can be converted into self-locking differentials by replacing the assembly within the existing housing with the assembly of this invention, without otherwise having to modify the housing or the other drive train parts.